Implement Kummer's transformations

[Rashid Rafeek]

julia> HypergeometricFunctions.M(0.5, 1.5, -1000)
NaN

This works correctly in scipy:

from scipy.special import hyp1f1

hyp1f1(0.5, 1.5, -1000)
0.02802495608198965

This used to not work in scipy too (scipy/scipy#2282) but was fixed in scipy/scipy#3022.

[Mikael Slevinsky]

Thanks! It seems to me that the issue is solved by implementing https://dlmf.nist.gov/13.7#E2, equivalently https://dlmf.nist.gov/13.2#E41 and https://dlmf.nist.gov/13.2#E42